1. Field of the Invention
The present invention relates to a method for detecting quantity variation of high purity liquid chemicals in semi-conductor producing processes, and more particular a method that randomly measures the capacitance of the chemicals to observe tiny variations in the quantity of the chemicals. This invention also discloses devices to perform this method.
2. Description of Related Art
In processes to produce integrated circuits or deposited chips mounted on silicon wafers, a lot of chemical depositing procedures and chemical etching procedures are used in the processes. In these procedures, various high purity liquid chemicals, acting as precursors, are bubbled to become vapors or directly liquid injected. Then, the vapors are mixed with a carrier gas or liquids and then fed into a reaction chamber to be deposited on chips or wafers. The high purity liquid chemicals also can be nebulized and directly injected into the reaction room by an injector or atomizer to carry out the chemical depositing procedures. Because the thickness of the deposited layers may only be from a fraction of a nanometer to hundreds of nanometers, not much of the liquid chemical is used. Therefore, containers used to hold the liquid chemicals also have a small volume usually in the range of tens of milliliters to tens of liters.
Because conventional containers have a conventional detecting device such as a float ball or an optical device having only two or three detecting points at low, lower and empty liquid levels, knowledge of quantity variations at any time during the depositing procedure is not available. If the detecting device fails at the low liquid level, the process operator will not be aware that the liquid chemicals are very nearly depleted which may cause damage when the liquid chemicals run out and the depositing procedures are incomplete. Furthermore, conventional detecting devices have bad sensitivity. Taking the float ball for example, the float ball is not suitable used in a bubbling container that has a violently agitating liquid or with a high viscosity liquid that may stick to the float ball and damp the response of the float ball or otherwise cause false indicating signal. The optical device is not suitable to detect liquid chemicals possessing dark colors or high viscosity.
Another conventional detecting device is a platform weight scale to weigh the liquid chemicals. However, pipelines of the container are immovable, and measurement of the platform weight scale is not precise especially when the weight ratio of the liquid chemicals to the container is very small.
According to the foregoing description, processes of producing semi-conductors still have a troublesome problem with regard to the use of high purity liquid but tiny amount of chemicals. Many depositing procedures have to estimate the quantity of liquid chemical remaining in the container based on prior experience to determine when the process should be suspended to check and replenish the liquid chemicals inside the containers or replace with new containers. Therefore, the efficiency and product quality of the machines is low and the risk of missed operation is high.
The present invention has arisen to mitigate and/or obviate the disadvantages of the conventional liquid chemical detecting devices.
The main objective of the method for detecting quantity variation of high purity liquid chemicals in accordance with the present invention is to be able to detect liquid levels instantly and continuously.
Another objective of the present invention is to provide a device to carry out the method to detect the liquid levels instantly and continuously.
Further benefits and advantages of the present invention will become apparent after a careful reading of the detailed description with appropriate reference to the accompanying drawings.